From owner-freebsd-hackers  Fri Jun  9 18:10:29 2000
Delivered-To: freebsd-hackers@freebsd.org
Received: from wantadilla.lemis.com (wantadilla.lemis.com [192.109.197.80])
	by hub.freebsd.org (Postfix) with ESMTP
	id A570337BBB5; Fri,  9 Jun 2000 18:10:20 -0700 (PDT)
	(envelope-from grog@wantadilla.lemis.com)
Received: (from grog@localhost)
	by wantadilla.lemis.com (8.9.3/8.9.3) id KAA82612;
	Sat, 10 Jun 2000 10:40:04 +0930 (CST)
	(envelope-from grog)
Date: Sat, 10 Jun 2000 10:40:03 +0930
From: Greg Lehey <grog@lemis.com>
To: "NandaKumar P.K." <p_k_nandan@yahoo.com>
Cc: FreeBSD Hackers <hackers@freebsd.org>
Subject: Re: IOCTL to the character driver is failing
Message-ID: <20000610104003.B81728@wantadilla.lemis.com>
References: <20000609072804.27088.qmail@web1903.mail.yahoo.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Mailer: Mutt 1.0pre2i
In-Reply-To: <20000609072804.27088.qmail@web1903.mail.yahoo.com>
Organization: LEMIS, PO Box 460, Echunga SA 5153, Australia
Phone: +61-8-8388-8286
Fax: +61-8-8388-8725
Mobile: +61-418-838-708
WWW-Home-Page: http://www.lemis.com/~grog
X-PGP-Fingerprint: 6B 7B C3 8C 61 CD 54 AF  13 24 52 F8 6D A4 95 EF
Sender: owner-freebsd-hackers@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

[moved to -hackers; this is an in-depth technical question]

On Friday,  9 June 2000 at  0:28:04 -0700, NandaKumar P.K. wrote:
> Hi,
>
> I am in the process of debugging my character driver
> interface to the RAID controller card. Lots of my
> IOCTLs i sent from the user code works with the driver
> but some IOCTLs are not reaching the driver. I found
> that one of the IOCTL that failed is having a size of
> data as 8096 bytes. Does FreeBSD has got any size
> restriction in IOCTL data size ? I know that there is
> no problem with Linux and Windows NT.

Indeed, you're limited to 4096 bytes.  From sys/ioccom.h:

#define	IOCPARM_MASK	0x1fff		/* parameter length, at most 13 bits */
#define	IOCPARM_MAX	PAGE_SIZE		/* max size of ioctl, mult. of PAGE_SIZE */

From sys/param.h:

#define PAGE_SHIFT	12		/* LOG2(PAGE_SIZE) */
#define PAGE_SIZE	(1<<PAGE_SHIFT)	/* bytes/page */

Even that is probably too big.  What are you trying to transfer that's
so big?

Greg
--
When replying to this message, please copy the original recipients.
For more information, see http://www.lemis.com/questions.html
Finger grog@lemis.com for PGP public key
See complete headers for address and phone numbers


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message